The long-term goal of this research is to understand the characteristics of the neurophysin-hormone system through crystallographic studies. A binary complex formed between bovine neurophysin II and L-phenylalanyl-L-tyrosine amide, a peptide known to bind neurophysin at its hormone binding site, has been crystallized, and is suitable for a crystallographic study. We will determine its structure, locate the peptide binding site and analyze the interactions between the protein and the peptide. We will also compare the structural details between the internally duplicated segments in neurophysin, and evaluate the magnitude and significance of the duplication in terms of its function. In addition to the study of this crystal, attempts will be made to crystallize bovine neurophysin complexes with the hormones, oxytocin and vasopressin. We also plan to isolate and purify neurophysin molecules from other species such as pig, sheep and horse, and to grow suitable crystals for x-ray diffraction studies. The aim is to study the detailed structures of several complexed and uncomplexed neurophysin molecules and to analyze their structural homology and differences. The proposed research could lead to a better understanding of the cooperative effect in the neurophysin-hormone system and the ligand-induced dimerization. It will also increase our knowledge concering the molecular basis of the specificity of neurophysin for posterior pituitary hormones, protein-polypeptide interactions, and protein dynamics in general.